Talk:Caledonian orogeny

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Untitled[edit]

I see from the Internet there seems to be some equivocation about what "Caledonian" should mean. Anyone know anything about that and care to introduce it as a problem?Botteville 00:09, 9 August 2005 (UTC)

It's quite precisely defined, see http://eprints.ouls.ox.ac.uk/archive/00000805/01/McKerrow_2000.pdf among others.
... a hypothetical series of events in geologic history explaining a group of highland formations that are very similar ... argh! This convoluted ... ahh, bit of prose, needs a major rewrite by a geologist. One more on my todo list - later :-) Vsmith 02:53, 9 August 2005 (UTC)

Assumptions?[edit]

There are many assumptions in this article regarding the references to the geological column which are put forward as facts. This is still theoretical as are all the dates. The geological column exists nowhere in the world! This article should be noted as being based on generally accepted, but unproven, theories. Refer definition empirical science and please apply.

Geodynamic history: comments[edit]

Armorica involved in the Caledonian orogeny

for earlier talk about this article by Mikenorton and me. - Woodwalker (talk)

Thanks for your edits. I wanted to work on Hercynian orogeny but found that before I could possibly do so, I had to take a look at the earlier (Caledonian) stuff first. Some comments: I would be in favour of having a separate article on tectonic phase (from tectonics), I will see if I have time to write something small (don't expect more than a stub and please feel free to add/link/correct).

Regarding this edit by Mike: pre-Pangaea paleogeography is a mess. Most of the time, it's difficult to find two authors agreeing on something. Before I started working on this article, I thought Caledonian referred to the closing of the Iapetus ocean, Hercynian/Variscan to the closure of the Rheic Ocean. It now seems to me I was wrong. Peter Ziegler in his atlas (1990, see the literature list for the ref) writes there was another continent involved (Armorica). In the first figure (thumbed to the right) in this article, I tried to express this by showing how (in Zieglers reconstructions) Armorica was already accreted to Laurussia/Euramerica in the Early Devonian (at 400 mya). The Caledonian orogeny then formed the Irish/Scottish Caledonides between Laurentia and Avalonia, the North-German/Polish Caledonides between Baltica and Avalonia and the Mid-European Caledonides (in other literature: Anglo-Brabant Caledonides) between Avalonia and Armorica. Ziegler is more or less backed in this by other authors:

  • Matte (2001): All of these authors agree on locating Armorica, like Avalonia, close to Gondwana in early Ordovician times. Nevertheless, its drift history is not so clear and differs according to the authors. For Van der Voo (1979) and Tait et al. (1997), Armorica drifted northward later than Avalonia, opening a very large ocean. For others, Armorica remained more or less closed to Gondwana during its northward drift, from Ordovician to Devonian times (Scotese and Golonka, 1992; Torsvik, 1998). In fact, Armorica is not defined precisely on the basis of palaeomagnetic data.
  • Torsvik et al (1996): The fate of the European massifs is as yet not well established though palaeomagnetic data clearly indicate that Armorica/Bohemia was at high latitudes together with Gondwana and Avalonia during the early Ordovician (Perroud et al. 1984; Torsvik et al., 1993a; Tait et al., 1994a). Armorica was probably peripheral to Gondwana throughout the Ordovician, whereas new palaeomagnetic data from Bohemia (Tait et al., 1995) indicate that Bohemia rifted off Gondwana during Mid-Ordovician times; this suggest that Armorica, Bohemia and Avalonia had disparate drift-histories. By the Caradoc, Bohemia had reached latitudes at around 40% and approximately 20% and adjacent to the Baltic Tomquist margin by Upper Silurian times (Tait et al., 1994b, 1995).
  • Franke (2000, in Geol.Soc.London Spec.Pub.; talks about the "Armorican Terrane Assemblage" or ATA): The evolution on the northern flank of the Variscides is complex. Narrowing of the Rheic Ocean between Avalonia and the ATA occurred during the late Ordovician through early Emsian, and was accompanied by formation of an oceanic island arc. By the early Emsian, the passive margin of Avalonia, the island arc and some northern part of the ATA were closely juxtaposed, but there is no tectonometamorphic evidence of collision.

Most of these authors are writing about the Hercynian orogeny. They seem to suggest that before this orogeny started, the Armorica/Bohemia pieces of the jigsaw puzzle were already in place. In fact, the coalbearing Devonian/Lower Carboniferous Rhenohercynian basin evolved as a backarc-basin on the southern margin of Laurussia/Euramerica, but in between Avalonian and Armorican terranes.

It thus seemed to me that Armorica (including Bohemia/Barrandia) was in the early Devonian (at least Emsian) already located at the southern margin of Laurussia/Euramerica. The actual collision, when these terranes were smashed on top of Laurussia, had to be waited for until the main phase of the Hercynian orogeny (around 310 mya, in the Carboniferous stage Westphalian) That would mean the Caledonian orogeny destroyed not only the Iapetus, but also at least part of the Rheic Ocean. This contradicts Mike's edit. I have no access to his source, but McKerrow at al (2002) define the Caledonian orogeny as: (only) those phases related to the closure of the Iapetus. I chose to ignore this, because they never mention the Mid-European or North-German/Polish Caledonides, maybe because their research is focussed on Ireland/Brittain(?).

Another source, Stampfli et al (2002), places the Armorican terranes still further south in the Early Devonian: There seems to be a contradiction between the inference that Armorica should have docked with Laurussia in Middle Devonian time and the final welding in Namurian time, after the closure of the Rheno-Hercynian domain. To reconcile these different lines of evidence, we propose that Armorica collided in Middle Devonian time with blocks detached from the Laurussian (Avalonian) margin during an Early Devonian rifting event. The latter led to the opening of the Rheno-Hercynian basin in the Emsian, within the southern passive margin of Laurussia. The oceanic nature of this basin (the Rheno-Hercynian ocean) is proven by the ophiolitic and pelagic remnants found in the Lizard, Giessen, and Harz nappes. (this fits with the last sentence from my citation of Franke (2000): but there is no tectonometamorphic evidence of collision)

The last seems an elegant compromise, but it does not explain the existence of the Mid-European/Anglo-Brabant Caledonides (Caledonian deformation is for example found in the Cambro-Ordovician massifs of the Ardennes). I am a bit confused. What to do...? Woodwalker (talk) 14:07, 23 October 2008 (UTC)

The source for my edit is here [1] (actually it's the 2006 paper by the same authors). I go for this because it combines both Palaeomag, facies and faunas, but the one thing that we do know is that none of these reconstructions can be regarded as definitive. Mikenorton (talk) 10:28, 24 October 2008 (UTC)
Nice article, that. I did not see it before. The least it shows us is that there is disagreement and uncertainty among authors on the position of Armorica during Ordovician to Devonian time. Note they put one half of the Armorican terranes (the eastern part: that's Perunica or Barrandia) closer to Laurussia, which explains some of the inconsistency. I found another article that was intended for the same publication: Ziegler & Dèzes (2005). It tells us the following about the Mid-European Caledonides:
The Mid-European Caledonides, that are exposed in the Ardennes and mark the Rheic suture between the Gondwana-derived East-Avalonia and the composite Armorican-Saxo-Thuringian terranes (Armorican Terrane Assembly; Pharaoh, 1999; Winchester & PACE, 2002; Verniers et al., 2002), were disrupted during the Early Devonian by back-arc extension, controlling the opening of the Rheno-Hercynian Basin and limited sea-floor spreading in its Lizzard and Giessen-Harz sub-basins.
I'd like to quote another source (I hope you don't mind me citing a lot. I think it helps to clear up and summarize things): Rey et al (1997, geol. soc. London spec. pub. 121, pp. 179-200), that tells us more about paleogeography:
The Variscan Belt of Europe resulted from the Early Devonian to Mid-Carboniferous collision of Laurussia and Gondwana, between which smaller Precambrian continental blocks (Avalonia, Armorica and its eastern equivalent, Barrandia, in Bohemia) were squeezed (e.g. Bard et al. 1980; Behr et al. 1984; Matte 1986, 1991; Franke 1989 a, b). The Gondwana-Laurussia convergence closed two oceanic domains of Cambrian to Ordovician age (Pin 1990): the Rheic ocean, between Avalonia and Armorica-Barrandia, and the Theic (McKerrow & Ziegler 1972) ocean (or Prototethys, including the Galicia-Massif Central ocean of Matte 1991) between Armorica-Barrandia and Gondwana. Their respective width is a point of contention (Neugebauer 1989). The collision of a Gondwana promontory (Iberia) with Laurussia s.l. (Baltica, Laurentia and Avalonia) formed the Ibero-Armorican arc, a salient orocline in the western part of the belt (Matte 1986; Burg et al. 1987). By the end of convergence, in Carboniferous times, the Variscan belt was characterized by the accretion of three main terranes (Avalonia, Armorica-Barrandia and Gondwana) with a bilateral symmetry centred on Armorica-Barrandia. Based on the direction of large scale thrust tectonics and the migration of the deformation and metamorphic events toward the forelands, it is inferred that the Rheic and Theic oceanic lithospheres were essentially consumed by subduction zones of opposite dip beneath the dorsal Armorica-Barrandia blocks (e.g. Matte 1986; Franke 1989 a, b).
To summarize:
  1. On Avalonia we can be sure: it was sutured to Baltica and Laurentia already at the Silurian-Devonian boundary.
  2. On the tectonic map of Europe, south of Avalonian crust we find a number of terranes that may or may not have shared a plate tectonic history to some extend, they include Armorica, Barrandia/Perunica, and others.
  3. The Rheic Ocean existed between Avalonia and Armorica, when it closed is uncertain. Some authors think Armorica was already close to Laurussia in the Early to Middle Devonian, others keep the ocean wide open until Gondwana collided with Laurussia and all of the small terranes were sandwiched in between.
  4. South of the Avalonia-derived London-Brabant massif, terranes are found that have been deformed during the Caledonian orogeny (Ordovician-Silurian). Some authors, among them Ziegler (1990) call these the Mid-European Caledonides. My map is based on this. Ziegler suggests they were formed by a Caledonian collision between Armorica and Avalonia, but that implies Armorica was already close to Laurussia in the Silurian. This contradicts your article by Cocks & Torsvik (2006). They think these terranes were part of the southern rim of Avalonia that rifted off Laurussia forming the Rhenohercynian basin, then collided with Laurussia again in an early phase of the Hercynian orogeny. On the other hand, if Armorica was still close to Gondwana in the Silurian and Early Devonian, how were these Mid-European Caledonides formed? Are they simply the southern part of the Caledonides found in Wales and Ireland?
I am searching further to find out. I think more of the uncertainty about Armorica's position should be reflected in the text and will try to adjust it (including my map) asap. Regards, Woodwalker (talk) 14:56, 24 October 2008 (UTC)
I have adjusted both the text and the map now to show there is no consensus in literature. Please check my edits and tell me if you agree. Woodwalker (talk) 11:01, 28 October 2008 (UTC)

Help with creation of North Sea Geological History[edit]

There is an effort to try to get the North Sea article passed to GA status, and a request was made by the reviewer for the geological history. An article has been roughly begun North Sea Geological History to summarize into the North Sea article. If anyone can help it would be greatly appreciated! SriMesh | talk 01:11, 22 November 2008 (UTC)

Definitions of Caledonides and Caledonoid[edit]

These two terms are used in Wikipedia and elsewhere but definitions are hard to come by and might benefit the lay reader. Anyone care to incorporate a definition within the article? (Same applies to Variscan orogeny and others of course). I'd venture that 'Caledonides' signifies 'the assemblage of rocks affected by and formed within the Caledonian orogeny together with the geological structures which arise from the event' but this seems clumsy and leaves open the question of boundaries. 'Caledonoid' I guess signifies structural trends but would benefit from an agreed definition - there must be one or more out there already!?
Geopersona (talk) 06:56, 17 January 2009 (UTC)

Please read this online book, at p 18 is a definition of Caledonian/Caledonoid. The first seems to indicate the orogenic era, the second structures with the same vergence. I am not familiar with the term "Caledonoid", but a google search on it gives many publications. Interestingly, they seem all older than the early 70s and seem all to be about the geology of the British Isles. I guess it is a pre-plate tectonics term, probably still used now and then but slowly disappearing from use.
Even if my guess is right and "Caledonoid" is only used regionally as well as becoming obsolete, I am still in favour of it having its own article. The term can be mentioned in this article too. Rather than in the header, it would be more fitting in a new section on the British Caledonides. I intended to write a paragraph summarizing the local geology for every part of the Caledonian belt later (Greenland/British Isles/Scandinavia/etc). Woodwalker (talk) 14:50, 17 January 2009 (UTC)
Thanks Woodwalker - uesful and interesting link. 'Caledonoid' is still with us (at least in UK) - see its use in the BGS regional guide to Wales, published 2007 where it's used to refer to later structures following lines set out during the Caledonian orogeny. I'll restrict it to that sense myself.
Geopersona (talk) 15:31, 17 January 2009 (UTC)

Scandian, Grampian, and Caladonian extant[edit]

From what I've gathered studying the subject, European writers tend to occasionally group the Taconic (Taconia-Laurentia) and often the Acadian (Avalonia-Laurentia) with the Caledonian (Baltica-Laurentia), while American authors see it as three separate yet related events (Even though Avalonia was docked to Baltica). I also understand the Scandian and Grampian not to be the same pulse with differing names but different pulses separated by an intermediate period in the Caledonian event caused by the oblique angle of impact. "The subduction culminated in plate collisions accompanied by mountain-building events known as the Caledonian Orogeny. The Caledonian Orogeny comprised three distinct phases: the Grampian phase (c. 480–465Ma), an intermediate phase (c. 465–435 Ma) for which there is no formal name, and the Scandian phase (c. 435–390 Ma)." - Open University SXR339 Chap5, Mountain Building in Scotland.Miglewis (talk) 14:22, 22 April 2009 (UTC)

What about the North American section?[edit]

The Appalachian Mountains of North America were part of the Caledonian orogeny...this article is too Euro-centric and needs to be broadened.Ryoung122 18:37, 11 May 2011 (UTC)

Things are even wider: Appalachian, Caledonian and Mauritanides mountain belts --Chris.urs-o (talk) 18:49, 11 May 2011 (UTC)